1. Field of the Invention
This invention relates to a semiconductor apparatus, and more particularly to a semiconductor apparatus based on a heterojunction structure of a nitride semiconductor.
2. Background Art
A nitride semiconductor device based on GaN has a larger bandgap than Si and a higher critical electric field. Hence, a small device with high breakdown voltage is realized more easily. The GaN-based semiconductor device used as a power semiconductor device has low on-resistance, realizing a low-loss device. Among others, a field effect transistor based on AlGaN/GaN heterojunction structure (see, e.g., JP-A 2007-059589 (Kokai)) has a simple device structure, showing promise for good characteristics.
Power devices based on wide bandgap semiconductors are currently under active research. However, while GaN and other nitride semiconductor devices achieve low on-resistance, characteristics specific to power devices such as avalanche capability are not taken into consideration in their design. This is because GaN-based devices are designed primarily for communication devices.